This invention relates to nuclear reactor control rod testing and in particular to an apparatus for testing the physical condition of finger type control rods.
The control rods which have operated within a nuclear reactor will suffer from radiation induced changes, as well as possible wear, cladding defects, swelling or ovality. In making a decision as whether to replace the rods or to continue their use, measurements must be made to evaluate potential defects.
Traditional eddy current examinations have used differential and absolute coils surrounding each rods for eddy current testing, as well as pancake proximity coils for determining the circumferential profile. It has been difficult to obtain accurate results with this traditional equipment. The control rod material property change caused by radiation is unknown, thereby introducing inaccuracies in eddy current measurement which depends on these properties. Even when a correcting calibration can be made for one portion of the control rod, errors are introduced in other portions of the control rod which have been exposed to different amounts of radiation, and which accordingly have different properties. These traditional pancake coils used to determine the profile of the rod have not been completely satisfactory.